1. Field of the Invention
This invention generally relates to the field of testing electronic circuits under operational temperatures. More particularly, the present invention relates to a method for controlled heating of electronic dynamic memory units.
2. Description of the Prior Art
Dynamic memory units exhibit degrading operation at a higher working temperature as the data retention capability and the access time are reduced. This reduction in data retention capability is due to the exponential increase in the memory cell's leakage current when the ambient temperature is increased. Such a reduction in the data retention capability of the dynamic memory cells necessitates a more frequent refresh activity. The access time, or the operational speed of the dynamic memory unit, decreases when the ambient temperature is increased due to the physical properties of the MOS/CMOS material and processes used to produce the memory units.
Therefore, it is well known in the art that memory units must be tested while subjected to their highest operating temperature. Although memory units do warm up during normal operation of their internal circuitry, they do not reach a sufficiently high temperature.
The most common method for such heating uses a controlled temperature oven. The memory unit is placed inside a special oven which is kept at the desired high temperature. The disadvantage of this method is that such an oven is fairly expensive and cumbersome which render it unsuitable for low cost, portable memory tester. Another major disadvantage of such heating is that when the memory unit is kept in the oven, it must be physically connected to the tester via a relatively long cable. This cable introduces distortions and propagation delays on the data signals. Yet a further disadvantage is that the memory module is heated from the outside so that it takes a certain period of time for the internal portion of the memory to reach the desired temperature.
Another method known to the art is to generate heat inside the memory unit by use of induction (e.g. controlled microwave radiation). While this method is faster than the oven method, all the remaining disadvantages as described above are also relevant with induction heating. Another further disadvantage typical of the induction heating method is that it may damage the memory unit when variations in the internal density of metallic/non-metallic components causes wrong distribution of the internal heat.